Dementia with Lewy bodies (DLB) is one of the most common neurodegenerative diseases and shares multiple clinical and neuropathological parallels with Alzheimer's (AD) and Parkinson's disease (PD). A variety of clinical signs are suggestive for the diagnosis, and imaging (βCIT SPECT) contributes substantially to the diagnosis. The study reported here was performed in search for a biomarker in the cerebrospinal fluid (CSF) of these patients. We applied 2D fluorescence difference gel electrophoresis and mass spectrometry to analyze the CSF proteome pattern of DLB patients after depleting twelve high-abundant proteins. The densitometric analysis of 2D gels showed the up- or down-regulation of 44 protein spots. Subsequently, 23 different proteins were identified. The majority is involved in acute phase and immune response. Many of these proteins were previously reported before as being associated with AD or PD, which strongly suggests a molecular cross-talk and may explain clinical and pathological overlap of these disease entities. Among the identified proteins are two highly upregulated proteins—inter alpha trypsin inhibitor heavy chain (ITIH4) and calsyntenin 1—that may have the potential to serve as molecular biomarkers specific for DLB. The identification of DLB-associated proteome changes will help to further understand pathological processes occurring in DLB and may provide future prospects to diagnostic and therapeutic options.